1. Field of the Invention
This invention relates to a stringing for a sports racket such as, but not limited to, a tennis racket or a racket-ball racket.
2. Background Information
Conventional sports rackets are strung with strings passed above and below each other to produce a woven string network. Since the strings are not bonded at their crossover points, the pattern of the string network may deform when the ball is struck by a racket with an upwards or downwards component of motion, such as that used by players wishing to place spin on the ball. The movement of the strings relative to one another produces wear through attrition and leads to premature string failure.
Conventional sports rackets are strung with strings with circular cross-sectional area. These strings are essentially long cylinders, and cylinders are aerodynamically categorized as bluff bodies. Hence, during the swinging motion of the racket, the air flowing through the string network produces large wakes behind each string, leading to significant aerodynamic drag that must be overcomed by additional work by the player.
Much of the prior art relating to the reduction or elimination of abrasion due to string motion introduces structural changes to the conventional string surface that maintain or increase the level of aerodynamic drag. For example, U.S. Pat. No. 4,249,731 (Amster) teaches grid members slidable on strings during the stringing process, the grid members bonded together to form a unitary grid. The grid members add thickness to the strings and increase substantially the drag. Furthermore, the tight fit that is necessary between the grid members and the strings to avoid rattling and energy losses during ball contact renders the stringing process difficult and impractical. U.S. Pat. No. 5,303,918 (Liu) teaches a string network wherein relative string motion is impaired by impregnating the ball-striking surface in an elastic covering after the ball-striking surface is formed by attaching the strings to the frame, essentially replacing the slidable grid members of U.S. Pat. No. 4,249,731 with an in situ casted material. The elastic covering more than doubles the effective thickness the strings, leading to a large and detrimental increases in aerodynamic drag. Furthermore, since racket stringing and re-stringing is commonly done at sports shops, this approach necessitates special molds, procedures and material know-how not available at sports shops.
Much of the prior art relating to string geometry introduces string crosssections having higher drag than a conventional string with circular cross-section and equal area. For example, U.S. Pat. No. 4,377,288 (Sulprizio), U.S. Pat. No. 4,597,576 (Haythornthwaite), and U.S. Pat. No. 4,462,591 (Kenworthy) present strings with noncircular cross-sections. In all three cases the strings are not streamlined since the strings, after mounting on the sports racket, have a higher drag than strings with circular cross section and equal cross-sectional area when the racket is swung in the usual manner.
U.S. Pat. No. 3,934,876 (Haddad) and U.S. Pat. No. 5,150,896 (Holmes) teach a racket with a ball-striking surface that is materially inseparable from the frame, and whose elements obtain the necessary rigidity through large cross-sectional area rather than through tension. As such, it is not possible for the racket user to tailor those playing properties of the racket normally selected through string tension, nor is it possible for the user to purchase a racket frame and a ball-striking surface independently from one another or replace the ball-striking surface in the event of damage.